Sighting devices have long been used to help shooters improve the placement of their small-arms weapons' fired shots. Small-arms weapons include those firearms that an individual may carry and use. Many handguns, for instance, include unmagnified iron sight devices with horizontal and vertical reference points that allow a shooter to align the gun parallel to the shooter's line of sight. Other firearms, such as carbines, rifles, assault rifles and light machine guns may include magnified sight devices (which are also known as telescopic sights, or scopes) to provide a shooter with improved accuracy in aligning the barrel with the intended target. These magnified sight devices are especially useful for hunters, sharpshooters, and others who find it advantageous to shoot at targets from a great distance. Successfully hitting any target depends on a shooter's ability to understand a bullet's likely flight path, or trajectory, before the bullet is fired.
Several factors influence the trajectory of a fired bullet, including those factors that are internal to the firearm and those factors that are external to the firearm. Factors internal to the firearm relate to the type of firearm and ammunition used. These are commonly referred to as ballistic characteristics. For instance, similar .22 caliber bullets will travel slightly different trajectories if fired from a revolver than if from a rifle because of differences in the ballistic characteristics between the revolver and the rifle. Also, different types of ammunition have different bullet shapes, casing sizes, and amounts of gunpowder. Each of these characteristics influences the performance of the ammunition. Understanding the characteristics of a particular firearm and particular ammunition is important to understanding the likely trajectory of a fired shot.
Factors external to the firearm which influence the trajectory of a bullet include the distance to a target (also known as range), wind, and other ambient environmental conditions. A fired bullet is under constant earthward acceleration due to gravity, and this is known as “bullet drop.” Bullet drop is characterized by a bullet path which curves increasingly toward the Earth over long ranges as the bullet falls to the ground. Therefore, in order to hit a faraway target, it is necessary to compensate for bullet drop by elevating the barrel of the firearm, and, thus, the aiming point. Wind is another factor that can influence bullet trajectory. It is recognized that a crosswind has the effect of deviating a bullet's trajectory resulting in offsets from the intended target seen at the aiming point. A crosswind along the path of the bullet has the effect of decreasing the effective range of the weapon since the bullet can be blown off course of its intended target at relatively close range. The deviation caused by wind increases as the wind velocity increases and as the range increases. Thus, understanding the distance to a target and the characteristics of any crosswinds are important to understanding the likely trajectory of a fired shot. Between the factors internal and external to a firearm, hitting a target at long range can be a challenge.
Because of this challenge, sharpshooters whose targets are very far away are often assisted by a spotter. A sharpshooter and a spotter together are often referred to as a shooting pair. The shooter operates the firearm by aiming it at a distant target and ultimately shooting a bullet. A spotter assists the shooter by measuring or estimating the distance to the target and observing wind velocity and direction, and then communicating this information to the shooter. A shooter then adjusts the aim of the firearm in view of this information with the goal of compensating for bullet drop and the influence of wind. The shooter then uses the firearm to shoot a bullet. In the event the shooter misses the target on the first shot, the spotter determines the hit point deviation from the aiming point, and relays this information to the shooter. If circumstances allow (i.e., the target has not moved), the shooter may then attempt subsequent shots. However, efficiency and stealth are highly prized by the shooting pair, so missed shots and multiple shots are undesirable. Thus, a need exists for technology that can improve the effectiveness of a shooter and spotter shooting pair.
Methods for measuring wind velocity have been developed, but are not optimal to the gun sight arts. Laser Doppler Velocimetry attempts to track the movement of the wind by tracking the motion of individual slices of the atmosphere. Such a system is particularly optimized for measuring the wind in the direction along the line-of-sight and by use of a clever receiving system, one could get an approximation of the cross wind. However, attempts to implement this practice with current shooting-pair concepts of operation have been unacceptable. Scintillometer statistics use a method that historically has implemented so-called “dual-ended” systems which require an illuminator and an imaging device or other set of detectors at opposite ends of the optical path in order to characterize the wind along the bullet trajectory. Applied to the gun sight arts, this method would require an imaging device located at the target, and for obvious reasons, such an arrangement would be impractical. A single-ended system, such as coherent Doppler Laser LIDAR, could be used, but it requires large collection apertures to detect laser guide stars. Such a system relies on aerosol backscatter, which is one practical method for measuring cross wind, but to this point has not been employed. In any event, implementation of such a system requires a powerful laser which could not be well maintained in the field. As such, prior art fails to disclose a single-ended system that is capable of meeting the objects of the present invention.
Thus, a need exists in the art for a compact sighting system that is capable of gathering accurate information including the distance to a target and a profile of the wind along the path to the target, and communicating corrective aiming instructions to a shooter.